In the 3rd Generation Partnership Project (3GPP), provisions of LTE-Advanced (Release 10, for example) which have been further evolved from the radio access scheme of Long Term Evolution (LTE) is under study.
For example, in Release 10 of LTE, eight mobile station (UE) categories (UE categories 1 to 8) according to communication rates in downlink and uplink are provided (see Non-Patent Document 1, for example). On the other hand, in Releases earlier than Release 10, specifically in Releases 8 and 9, five UE categories (UE categories 1 to 5) are provided. In other words, UE categories 6 to 8 which can achieve faster communication rates than UE categories 1 to 5 have been added to Release 10.
It is provided that a mobile station supporting UE categories 6 to 8 notifies a radio base station (eNB) of both UE categories (1 to 5) in Releases 8, 9 and UE categories (6 to 8) which have been added in Release 10. This enables the radio base station to perform radio communications with a mobile station even if the radio base station does not support Release 10.
Further, for soft buffer size (Total num. of soft channel bits) which a mobile station should be equipped with, a different value is provided for each UE category from the standpoint of ensuring throughput.